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(86.6): J.F. Seely, J.O. Ekberg, C.M. Brown, U. Feldman, W.E. Behring, J. Reader and M.C. Richardson, Phys. Rev. Letters, U.S.A., 1986, 17, 2924-7.

(87.3): J.O. Ekberg, U. Feldman, J.F. Seely, C.M. Brown, J. Reader and N. Acquista, J. opt. Soc. Am. B, 1987, 4, 1913-8.